This invention relates to a corrosion resistant, ferritic alloy and more particularly to such an alloy having a novel combination of magnetic and electrical properties and corrosion resistance.
Heretofore, silicon-iron alloys and ferritic stainless steels have been used for the manufacture of magnetic cores for relays and solenoids. Silicon-iron alloys contain up to 4% silicon and the balance is essentially iron. Such alloys have excellent magnetic properties but leave much to be desired with respect to corrosion resistance. Ferritic stainless steels, on the other hand, such as AISI Type 430F, provide excellent corrosion resistance, but leave something to be desired with respect to magnetic properties, particularly the saturation induction property. Saturation induction, or saturation magnetization as it is sometimes referred to, is an important property in a magnetic material because it is a measure of the maximum magnetic flux that can be induced in an article, such as an induction coil core, made from the alloy. Alloys with a low saturation induction are less than desirable for making such cores because a larger cross-section core is required to provide a given amount of magnetic attraction force as compared to a material with a high saturation induction. In other words, low saturation induction in a core material limits the amount of size reduction which can be accomplished in the design of relays and solenoids.
The increasingly frequent use of such automotive technologies as fuel injection, anti-lock braking systems, and automatically adjusting suspension systems in late model automobiles has created a need for a magnetic material having good corrosion resistance but higher saturation induction than known ferritic stainless steels. The need for good corrosion resistance is of particular importance in automotive fuel injection systems in view of the introduction of more corrosive fuels such as those containing ethanol or methanol.
In an attempt to provide materials having a combination of corrosion resistance, good magnetic properties, and good machinability the following alloys were developed. The alloys, designated QMRlL, QMR3L, and QMR5L, have the following nominal compositions in weight percent.
______________________________________ wt. % QMR1L QMR3L QMR5L ______________________________________ Si 2 0.4 1.5 Cr 7 13 15 Al 0.6 1 1 Fe Bal. Bal. Bal. ______________________________________
Each of the alloys also includes lead for the reported purpose of improving machinability.
U.S. Pat. No. 3,925,063 issued to Kato et al. on Dec. 9, 1975 relates to a corrosion resistant, magnetic alloy which includes a small amount of lead, calcium and/or tellurium for the purpose of improving the machinability of the alloy. The alloy has the following broad range in weight percent:
______________________________________ wt. % ______________________________________ C 0.08 max. Si 0-6 Cr 10-20 Al 0-5 Mo 0-5 ______________________________________
at least one of the following are included: 0.03-0.40% lead, 0.002-0.02% calcium, or 0.01-0.20% tellurium; and the balance is essentially iron.
U.S. Pat. No. 4,705,581 issued to Honkura et al. on Nov. 10, 1987 relates to a silicon-chromium-iron, magnetic alloy having some corrosion resistance. The alloy has the following broad range in weight percent:
______________________________________ wt. % ______________________________________ C 0.03 max. Mn 0.40 max. Si 2.0-3.0 S 0-0.050 Cr 10-13 Ni 0-0.5 Al 0-0.010 Mo 0-3 Cu 0-0.5 Ti 0.05-0.20 N 0.03 max. ______________________________________
and the balance essentially iron wherein C+N.ltoreq.0.05%, and at least one of the following is included: 0.015-0.045% lead, 0.0010-0.0100% calcium, 0.010-0.050% tellurium or selenium.
U.S. Pat. No. 4,714,502 issued to Honkura et al. on Dec. 22, 1987 relates to a magnetic alloy having some corrosion resistance and which is reported to be suitable for cold forging. The alloy has the following broad range in weight percent:
______________________________________ wt. % ______________________________________ C 0.03 max. Mn 0.50 max. Si 0.04-1.10 S 0.010-0.030 Cr 9.0-19.0 Ni 0-0.5 Al 0.31-0.60 Mo 0-2.5 Cu 0-0.5 Ti 0.02-0.25 Pb 0.10-0.30 Zr 0.02-0.10 N 0.03 max. ______________________________________
and the balance essentially iron wherein C+N .ltoreq.0.040%, Si+Al.ltoreq.1.35%, and at least one of the following is included: 0.002-0.02% calcium, 0.01-0.20% tellurium, or 0.010-0.050% selenium.
The foregoing alloys include combined levels of chromium, silicon, and aluminum such that the alloys provide lower than desired saturation induction. The relatively high silicon and aluminum in some of those alloys also indicates that those alloys would have less than desirable malleability. Furthermore, all of the foregoing alloys contain lead which is known to present environmental and health risks in both alloy production and parts manufacturing.